Squamous cell cancer of the anus (SCCA) is one of the most common cancers among aging HIV-infected individuals in the United States. HIV-infected persons are at 40-80-times higher risk for SCCA than the general population, and recent cohort studies report that the incidence of SCCA among HIV-infected men is between 49-144/100,000 person-years, which is substantially higher than the incidence of cervical cancer prior to widespread screening with cervical cytology. The alarming increase in anal precancer and cancer in HIV- infected individuals has led to an increased emphasis on prevention. Current HIV primary care Guidelines (NY state HIV primary care guidelines, HIV Medical Association, and Infectious Diseases Society of America) both recommend annual anal cytology screening, with triage to high resolution anoscopy (HRA)-guided biopsy for histologic confirmation of anal high grade intraepithelial lesions (HSIL) among HIV-infected men who have sex with men (MSM), and certain HIV-infected women. However, HRA-guided histologic diagnosis of HSIL is resource intensive, and has several drawbacks, including: extensive clinician expertise/training; pathology cost, availability, interpretation expertise; separate patient visits for diagnosis and treatment; and patient discomfort associated with unnecessary, non-neoplastic biopsies, given the low specificity of HRA-based visual HSIL identification. Our group has developed a portable, battery-operated, high-resolution microendoscope (mHRME) that provides subcellular images of the anal epithelium, delineating the cellular and morphologic changes associated with neoplasia. Our central hypothesis is that this 'optical' approach will increase the efficiency, clinical impact, and cost-effectiveness of the current standard of HRA-guided biopsy. In a recent pilot trial, the mHRME demonstrated a high sensitivity and specificity of anal HSIL diagnosis (94% and 92% respectively) compared to anal biopsy. Based on our significant preliminary data, we now propose to optimize and validate 3D imaging and HRME with a software interface that provides real- time image interpretation assistance, thus facilitating usage by less-experienced clinicians in community-based or low-resource settings. To validate this, we will conduct a study to determine the efficiency and diagnostic characteristics of an mHRME 'optical biopsy' approach versus the current standard of HRA-based tissue biopsy. In addition, we will construct, refine and analyze a disease model of HRA-based screening with mHRME to determine the cost- effectiveness of incorporating HRME into HRA-based HSIL diagnosis. Successful results will allow for improved efficacy and resource utilization for cancer screening in HIV-infected individuals for anal cancer and other epithelial cancers including the cervix, oral cavity, bladder, and GI tract.